smooth muscle

smooth mus·cle

one of the involuntary muscle fibers of the internal organs, blood vessels, and other body structures not under direct control of the will; contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei and a length of 20-200 mcm, or even longer in the pregnant uterus; although transverse striations are lacking, both thick and thin myofibrils occur; smooth muscle fibers are bound together into sheets or bundles by reticular fibers, and frequently elastic fiber nets are also abundant.See also: involuntary muscles.

smooth muscle

n.

Muscle tissue that contracts without conscious control, having the form of thin layers or sheets made up of spindle-shaped, unstriated cells with single nuclei and found in the walls of the internal organs, such as the stomach, intestine, bladder, and blood vessels, excluding the heart.

smooth muscle

Etymology: AS, smoth

one of three kinds of muscle, composed of elongated, spindle-shaped cells in muscles not under voluntary control, such as the smooth muscle of the intestines, stomach, and other viscera. The nucleated cells of smooth muscle are arranged parallel to one another and to the long axis of the muscle they form. Smooth muscle fibers are shorter than striated muscle fibers, have only one nucleus per fiber, and are smooth in appearance. Biofeedback devices may help many people gain partial control of contractions of involuntary smooth muscles. Also called involuntary muscle, unstriated muscle. Compare cardiac muscle, striated muscle .

Smooth muscle

smooth mus·cle

(smūdh mŭs'ĕl)

One of the muscle fibers of the internal organs, blood vessels, hair follicles; contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei and a length from 20-200 mcm, or even longer in the pregnant uterus; although transverse striations are lacking, both thick and thin myofibrils occur; such fibers are bound together into sheets or bundles by reticular fibers, and frequently elastic fiber nets are also abundant. See also: involuntary muscles

smooth muscle

The unstriped involuntary muscle occurring in the walls of blood vessels, the intestines and the bladder, and controlled by the AUTONOMIC NERVOUS SYSTEM and by HORMONES.

muscle

contractile soft tissue, responsible for all significant active movements and force-generations in an animal body. Divisible into three classes: (1) skeletal or voluntary muscle the class of muscle acting, in almost all body locations, to move one bone relative to another, the more superficial skeletal muscles being visible under the skin in all but the most obese subjects; (2) cardiac muscle the type unique to the heart; (3) smooth muscle composing the actively adjustable components of the walls of blood vessels and of the gastrointestinal, respiratory, urinary and reproductive tracts. Skeletal and cardiac are the striated muscles; cardiac and smooth share the property of being involuntary. See alsomuscle fibres, muscle fibre types, myofibrils; Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7.

smooth mus·cle

(smūdh mŭs'ĕl)

One of the muscle fibers of the internal organs, blood vessels, hair follicles.

muscle

an organ composed of bundles of fibers that has the power to contract and hence to produce movement. Muscles are responsible for locomotion and help support the body, generate heat and perform a number of other functions. They are of two varieties: striated (or striped, voluntary or skeletal), which makes up most of the meat of a carcass, and smooth (unstriated), which includes all the involuntary muscle of the viscera, heart and blood vessels.

Skeletal muscle fibers range in length from a few millimeters to many centimeters. They also vary in color from white to deep red. Each muscle fiber receives its own nerve impulses, which trigger fine and varied motions. At the signal of an impulse traveling down the nerve, the muscle fiber changes chemical energy into mechanical energy, and the result is muscle contraction. At least two major types of muscle fiber have been identified by histochemical techniques: type I (red) fibers, which have a slow contraction; and type II (white) fibers, which have a fast contraction.

Some muscles are attached to bones by tendons. Others are attached to other muscles, and to skin, producing, for example, the skin twitch, the eye blink and hair erection. Parts of the walls of hollow internal organs, such as the heart, stomach and intestines and also blood vessels, are composed of muscles. See also muscular. For a complete list of named muscles see Table 13.

agonistic muscle

prime mover; a muscle opposed in action by another muscle, called the antagonist.

antagonistic muscle

one that counteracts the action of another muscle (the agonist).

appendicular muscle

one of the muscles of a limb.

arrector pili muscle

small, smooth muscle attached to the bulb of the hair which causes erection of the hair and compression of the attending sebaceous gland when it contracts.

arterial muscle

part of the tunica media; smooth muscle fibers arranged in a circular pattern around the lumen.

the muscle may have torn away from its insertion, in which case the tendon will be slack, or it may be a complete or partial separation of the belly of the muscle, when the muscle will be swollen and hard. Structural and conformational changes may result, e.g. in rupture of the gastrocnemius muscle, and the hernias caused by rupture of the ventral abdominal muscles or the diaphragm.

skeletal m's

striated muscles that are attached to bones and typically cross at least one joint. Called also voluntary or striated muscles.

a relative deficiency of type II muscle fibers, with a predominance of type I fibers. An inherited defect in Labrador retrievers. Clinical signs include stunted growth, and muscle weakness and abnormal gait, which subside with rest, from an early age.

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